1. Field of the Invention
This application relates to portland cement concrete articles of increased strength prepared by impregnating the articles with aqueous solutions of alkali metal or alkaline earth metal polysulfide and heating them.
Portland cement concrete has become the world's largest bulk building material. The concrete comprises an admixture of portland cement with sand and aggregate (gravel or crushed stone). It is generally formed by mixing portland cement, water, sand and gravel or crushed stone, and allowing the mixture to harden to form a dense structure. The character of the "paste" mixture of water and cement is generally held to determine the important engineering properties of the concrete.
Construction concrete is generally formulated to contain from about 5 to 30 weight percent cement based upon the dry weight of materials. Generally, higher cement content (in the upper range of the usual content) produces concrete of higher strength.
Recently, shortages of cement in many parts of the world make particularly attractive the prospects of supplying concrete of low cement content which has high strength.
2. Description of the Prior Art
Polymer cements and polymer-impregnated concretes are known. The former usually contain a latex such as polyvinyl chloride, polyvinyl acetate, acrylonitrite-butadiene-styrene, etc., or an acrylic in solid or liquid form.
U.S. Pat. No. 2,820,713 discloses mortar compositions containing minor amounts of methyl cellulose and alkaline earth polysulfides and/or bunte salts as adhesion improvers.
U.S. Pat. Nos. 2,962,467 and 3,198,644 disclose similar mortar compositions.
"Characteristics of Portland Cement from the Gypsum-Sulfuric Acid Process" by Fredrich Wolfe and Joachim Hille (Silikattechnik, 1967, 1812), pages 55-57, discusses the effect on certain portland cements by the addition of calcium sulfide (Ca .sub.2 S).